Hybrid vehicle

ABSTRACT

A hybrid vehicle includes a transmission unit and a clutch. The transmission unit is configured to be able to switch into a neutral state. The hybrid vehicle is able to transmit power of an engine through any one of a first path through which power is transmitted to a first MG from the engine via the transmission unit and a differential unit and another second path through which power is transmitted from the engine. The clutch is provided in the second path. The clutch switches between an engaged state where power is transmitted and a released state where transmission of power is interrupted. The controller sets the transmission unit to the neutral state and sets the clutch to the engaged state, and then starts the engine by increasing the rotation speed of the engine with the use of the first MG.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hybrid vehicle and, more particularly, to a hybrid vehicle including first and second rotary electric machines and a transmission unit.

2. Description of Related Art

There is known a hybrid vehicle including not only an engine, two rotary electric machines and a power split mechanism but also a transmission mechanism between the engine and the power split mechanism.

A hybrid vehicle described in International Application Publication No. 2013/114594 employs a series-parallel hybrid system. In the vehicle having a series-parallel hybrid system, the power of an engine is transmitted to a first rotary electric machine (first motor generator) and is used to generate electric power, while part of the power of the engine is also transmitted to drive wheels via a power split mechanism.

There is also known a hybrid vehicle having a configuration (series hybrid system) by which the hybrid vehicle generates electric power by the use of the power of an engine and travels in series mode in which a motor is driven by the generated electric power. In this series hybrid system, the power of the engine is not transmitted to drive wheels.

The hybrid vehicle described in International Application Publication No. 2013/114594 is not able to travel in series mode because the power of the engine is also transmitted to the drive wheels via the power split mechanism at the time when the power of the engine is transmitted to the first motor generator.

In the series-parallel hybrid system, there is a concern that tooth contact noise occurs in a gear mechanism provided in a drive system between the engine and the drive wheels because of torque fluctuations of the engine at a low vehicle speed, or the like, so it is required to select an operating point of the engine such that tooth contact noise does not occur, and the engine may be operated at an operating point at which fuel consumption is not optimal. Therefore, there is room for improvement in fuel consumption.

On the other hand, in the series hybrid system, the engine is completely isolated from a gear mechanism provided in a drive system, so such tooth contact noise does not need to be considered so much. However, the entire torque of the engine is once converted to electric power and then the electric power is converted back to the torque of the drive wheels with the motor, so the series hybrid system is inferior in fuel consumption in a speed range in which the operation efficiency of the engine is high to the series-parallel hybrid system.

In this way, there is a point in which the series hybrid system is superior to the series-parallel hybrid system and there is also a point in which the series-parallel hybrid system is superior to the series hybrid system, so it is desirable to be configured to allow one of the series mode and the series-parallel mode to be selected in response to the condition of a vehicle.

When such a hybrid vehicle that is able to perform both the series mode and the series-parallel mode is implemented, if the engine is started by the first motor generator while the power transmission unit (transmission unit) is placed in a non-neutral state where the output from the engine is transmittable to a side downstream of the power transmission unit as is performed in the vehicle described in International Application Publication No. 2013/114594, an engine startup shock may be transmitted to an output shaft coupled to wheels and a shock that is experienced by a driver may increase.

SUMMARY OF THE INVENTION

The invention provides a hybrid vehicle that is able to travel in both series mode and series-parallel mode and that is directed to achieve both a reduction in engine startup shock and the response of the vehicle.

An aspect of the invention provides a hybrid vehicle. The hybrid vehicle includes an internal combustion engine, a first rotary electric machine, a second rotary electric machine, a power transmission unit, a differential unit, a clutch and a controller. The second rotary electric machine is configured to output power to a drive wheel. The power transmission unit includes an input element and an output element. The input element is configured to receive power from the internal combustion engine. The output element is configured to output power input to the input element. The power transmission unit is configured to switch between a non-neutral state where power is transmitted between the input element and the output element and a neutral state where power is not transmitted between the input element and the output element. The differential unit includes a first rotating element, a second rotating element and a third rotating element. The first rotating element is connected to the first rotary electric machine. The second rotating element is connected to the second rotary electric machine and the drive wheel. The third rotating element is connected to the output element. The differential unit is configured such that, when rotation speeds of any two of the first rotating element, the second rotating element and the third rotating element are determined, a rotation speed of the remaining one of the first rotating element, the second rotating element and the third rotating element is determined. The clutch is configured to switch between an engaged state where power is transmitted from the internal combustion engine to the first rotary electric machine and a released state where transmission of power from the internal combustion engine to the first rotary electric machine is interrupted. Power from the internal combustion engine is transmitted to the first rotary electric machine through at least one of a first path or a second path. The first path is a path through which power is transmitted from the internal combustion engine to the first rotary electric machine via the power transmission unit and the differential unit. The second path is a path through which power is transmitted from the internal combustion engine to the first rotary electric machine via a path different from the first path. The clutch is provided in the second path. The controller is configured to control the internal combustion engine, the first rotary electric machine, the power transmission unit and the clutch. The controller is configured to: (i) set the power transmission unit to the neutral state, (ii) set the clutch to the engaged state, and (iii) then start the internal combustion engine by increasing a rotation speed of the internal combustion engine with the use of the first rotary electric machine.

With the thus configured hybrid vehicle, by starting the internal combustion engine as in the case of control that is executed by the controller, a shock at a startup of the internal combustion engine is cut off by the power transmission unit placed in the neutral state and is not transmitted to the drive wheel. Therefore, it is possible to reduce a shock at a startup of the internal combustion engine, which is experienced by a user.

In the hybrid vehicle, the controller may be configured to use any one of a first startup method for the internal combustion engine and a second startup method for the internal combustion engine in response to a state of the vehicle. The first startup method may be executed while the power transmission unit is set to the non-neutral state. The second startup method may be executed while the power transmission unit is set to the neutral state, the clutch is set to the engaged state and then the rotation speed of the internal combustion engine is increased with the use of the first rotary electric machine.

In the hybrid vehicle, the controller may be configured to cause the vehicle to travel in a selected one of a plurality of operation modes. The plurality of operation modes may include a series-parallel mode and a series mode. The series-parallel mode may be a mode in which the power transmission unit is set to the non-neutral state and the clutch is set to the released state. The series mode may be a mode in which the power transmission unit is set to the neutral state and the clutch is set to the engaged state. The controller may be configured to use the first startup method when the operation mode after a startup of the internal combustion engine is set to the series-parallel mode, and use the second startup method when the operation mode after a startup of the internal combustion engine is set to the series mode.

In the hybrid vehicle, the controller may be configured to change an operation characteristic of the vehicle based on one of the operation modes, which is selected through switch operation of the user. The operation modes may include a first mode and a second mode. The first mode may be an operation mode having a higher acceleration response of the vehicle than the second mode. The controller may be configured to use the first startup method when the user selects the first mode, and use the second startup method when the user selects the second mode.

A user may place importance on increasing the response of the vehicle rather than reducing a shock at a startup of the internal combustion engine. With control that is executed by the controller of the hybrid vehicle, a vehicle adapted to user's taste on a startup of the internal combustion engine is implemented.

In the hybrid vehicle, the controller may be configured to cause the vehicle to travel in a selected one of a plurality of operation modes. The plurality of operation modes may include a first mode and a second mode. The first mode may be a mode, in which control is executed such that a rotation speed of the first rotary electric machine is zero. The second mode may be a mode in which the rotation speed of the first rotary electric machine changes in response to a vehicle speed. The controller may be configured to use the second startup method when a rotation speed of the third rotating element is higher than a predetermined value, and use the first startup method when the rotation speed of the third rotating element is lower than or equal to the predetermined value.

The startup method that shortens a startup time may vary depending on the operation mode of the vehicle before a startup of the internal combustion engine. Therefore, as in the case of control in the hybrid vehicle, by selecting the startup method for the internal combustion engine commensurately with the operation mode before a startup of the internal combustion engine, it is possible to shorten the startup time of the internal combustion engine.

With the above-described configuration of the hybrid vehicle that is an example of an embodiment of the invention, it is possible to achieve both a reduction in engine startup shock and the response of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a view that shows the overall configuration of a hybrid vehicle including a drive system according to an embodiment of the invention;

FIG. 2 is a block diagram that schematically shows power transmission paths of components of the vehicle in FIG. 1;

FIG. 3 is a block diagram that shows the configuration of a controller for the vehicle in FIG. 1;

FIG. 4 is a view that schematically shows the configuration of a hydraulic circuit mounted on the hybrid vehicle shown in FIG. 1;

FIG. 5 is a chart that shows each drive mode in the hybrid vehicle and controlled statuses of clutch and brake of a transmission unit in each drive mode;

FIG. 6 is a nomograph in one-motor EV mode that is one of the drive modes shown in FIG. 5;

FIG. 7 is a nomograph in two-motor EV mode that is one of the drive modes shown in FIG. 5;

FIG. 8 is a nomograph in series-parallel HV mode that is one of the drive modes shown in FIG. 5;

FIG. 9 is a nomograph in series HV mode that is one of the drive modes shown in FIG. 5;

FIG. 10 is a chart that shows controlled statuses of the clutch and brake of the transmission unit in each drive mode according to an alternative embodiment to the embodiment;

FIG. 11 is a nomograph for illustrating operations of E4 line and E5 line among the drive modes according to the alternative embodiment shown in FIG. 10;

FIG. 12 is a nomograph for illustrating operations of H6 line to H8 line among the drive modes according to the alternative embodiment shown in FIG. 10;

FIG. 13 is a flowchart that shows the details of a first example of engine startup control that is executed by the controller according to the present embodiment;

FIG. 14 is a view that shows an example of a mode determination map that is used in step S20 of the flowchart;

FIG. 15 is an operation waveform chart that shows an example of an engine startup of the hybrid vehicle;

FIG. 16 is a flowchart that shows the details of a second example of engine startup control that is executed by the controller;

FIG. 17 is a table that illustrates the correspondence relationship between a pre-engine startup state of the hybrid vehicle and an engine startup state;

FIG. 18 is a nomograph for illustrating an engine startup in one-motor EV mode shown in K1 line in FIG. 17.

FIG. 19 is a nomograph for illustrating an engine startup in one-motor EV mode shown in K2 line in FIG. 17; and

FIG. 20 is a nomograph for illustrating an engine startup in two-motor EV mode shown in K3 line in FIG. 17.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. Like reference numerals denote the same or corresponding portions in the following embodiment, and the description thereof will not be repeated.

FIG. 1 is a view that shows the overall configuration of a hybrid vehicle including a drive system according to the embodiment of the invention.

As shown in FIG. 1, the hybrid vehicle 1 (hereinafter, also referred to as vehicle 1) includes an engine 10, the drive system 2, drive wheels 90 and a controller 100. The drive system 2 includes a first motor generator (hereinafter, referred to as first MG) 20 that is a first rotary electric machine, a second motor generator (hereinafter, referred to as second MG) 30 that is a second rotary electric machine, a transmission unit 40, a differential unit 50, a clutch CS, an input shaft 21, a counter shaft 70 that is an output shaft of the drive system 2, a differential gear set 80 and a hydraulic circuit 500.

The hybrid vehicle 1 is a front-engine front-drive (FF) hybrid vehicle that travels by using the power of at least any one of the engine 10, the first MG 20 and the second MG 30. The hybrid vehicle 1 may be a plug-in hybrid vehicle of which an in-vehicle battery (not shown) is rechargeable from an external power supply.

The engine 10 is, for example, an internal combustion engine; such as a gasoline engine and a diesel engine. Each of the first MG 20 and the second MG 30 is, for example, a permanent magnet synchronous motor that includes a rotor in which permanent magnets are embedded. The drive system 2 is a double-axis drive system in which the first MG 20 is provided along a first axis 12 coaxial with the crankshaft of the engine 10 and the second MG 30 is provided along a second axis 14 different from the first axis 12. The first axis 12 and the second axis 14 are parallel to each other.

The transmission unit 40, the differential unit 50 and the clutch CS are further provided along the first axis 12. The transmission unit 40, the differential unit 50, the first MG 20 and the clutch CS are arranged from the side close to the engine 10 in the stated order.

The first MG 20 is provided so as to be able to receive power from the engine 10. More specifically, the input shaft 21 of the drive system 2 is connected to the crankshaft of the engine 10. The input shaft 21 extends along the first axis 12 in a direction away from the engine 10. The input shaft 21 is connected to the clutch CS at its distal end extending from the engine 10. A rotary shaft 22 of the first MG 20 extends in a cylindrical shape along the first axis 12. The input shaft 21 passes through the inside of the rotary shaft 22 at a portion before the input shaft 21 is connected to the clutch CS. The input shaft 21 is connected to the rotary shaft 22 of the first MG 20 via the clutch CS.

The clutch CS is provided in a power transmission path from the engine 10 to the first MG 20. The clutch CS is a hydraulic friction engagement element that is able to couple the input shaft 21 to the rotary shaft 22 of the first MG 20. When the clutch CS is placed in an engaged state, the input shaft 21 and the rotary shaft 22 are coupled to each other, and transmission of power from the engine 10 to the first MG 20 is allowed. When the clutch CS is placed in a released state, coupling of the input shaft 21 to the rotary shaft 22 is released, and transmission of power from the engine 10 to the first MG 20 via the clutch CS is interrupted.

The transmission unit 40 shifts power from the engine 10 and then outputs the power to the differential unit 50. The transmission unit 40 includes a single-pinion-type planetary gear mechanism, a clutch C1 and a brake B1. The single-pinion-type planetary gear mechanism includes a sun gear S1, pinions P1, a ring gear R1 and a carrier CA1.

The sun gear S1 is provided such that the rotation center of the sun gear S1 coincides with the first axis 12. The ring gear R1 is provided coaxially with the sun gear S1 on the radially outer side of the sun gear S1. The pinions P1 are arranged between the sun gear S1 and the ring gear R1, and are in mesh with the sun gear S1 and the ring gear R1. The pinions P1 are rotatably supported by the carrier CA1. The carrier CA1 is connected to the input shaft 21, and rotates integrally with the input shaft 21. Each of the pinions P1 is provided so as to be revolvable about the first axis 12 and rotatable around the central axis of the pinion P1.

As shown in FIG. 6 to FIG. 9, FIG. 11 and FIG. 12 (described later), the rotation speed of the sun gear S1, the rotation speed of the carrier CA1 (that is, the rotation speed of the engine 10) and the rotation speed of the ring gear R1 are in the relationship represented by points that are connected by a straight line in each of the nomographs (that is, the relationship that, when any two rotation speeds are determined, the remaining one rotation speed is also determined).

In the present embodiment, the carrier CA1 is provided as an input element to which power is input from the engine 10, and the ring gear R1 is provided as an output element that outputs the power input to the carrier CA1. By the use of the planetary gear mechanism including the sun gear S1, the pinions P1, the ring gear R1 and the carrier CA1, power input to the carrier CA1 is shifted and output from the ring gear R1.

The clutch C1 is a hydraulic friction engagement element that is able to couple the sun gear S1 to the carrier CA1. When the clutch C1 is placed in an engaged state, the sun gear S1 and the carrier CA1 are coupled to each other, and rotate integrally with each other. When the clutch C1 is placed in a released state, integral rotation of the sun gear S1 and the carrier CA1 is cancelled.

The brake B1 is a hydraulic friction engagement element that is able to restrict (lock) the rotation of the sun gear S1. When the brake B1 is placed in an engaged state, the sun gear S1 is fixed to the case body of the drive system, and the rotation of the sun gear S1 is restricted. When the brake B1 is placed in a released state (disengaged state), the sun gear S1 is separated from the case body of the drive system, and the rotation of the sun gear S1 is allowed.

A speed ratio (the ratio of the rotation speed of the carrier CA1 that is the input element to the rotation speed of the ring gear R1 that is the output element, specifically, Rotation Speed of Carrier CA1/Rotation Speed of Ring Gear R1) of the transmission unit 40 is changed in response to a combination of the engaged/released states of the clutch C1 and brake B1. When the clutch C1 is engaged and the brake B1 is released, a low gear position Lo in which the speed ratio is 1.0 (directly coupled state) is established. When the clutch C1 is released and the brake B1 is engaged, a high gear position Hi in which the speed ratio is smaller than 1.0 (for example, 0.7, and a so-called over-drive state) is established. When the clutch C1 is engaged and the brake B1 is engaged, the rotation of the sun gear S1 and the rotation of the carrier CA1 are restricted, so the rotation of the ring gear R1 is also restricted.

The transmission unit 40 is configured to be able to switch between a non-neutral state and a neutral state. In the non-neutral state, power is transmitted. In the neutral state, power is not transmitted. In the present embodiment, the above-described directly coupled state and over-drive state correspond to the non-neutral state. On the other hand, when both the clutch C1 and the brake B1 are released, the carrier CA1 is allowed to coast about the first axis 12. Thus, the neutral state in which power transmitted from the engine 10 to the carrier CA1 is not transmitted from the carrier CA1 to the ring gear R1 is obtained.

The differential unit 50 includes a single-pinion-type planetary gear mechanism and a counter drive gear 51. The single-pinion-type planetary gear mechanism includes a sun gear S2, pinions P2, a ring gear R2 and a carrier CA2.

The sun gear S2 is provided such that the rotation center of the sun gear S2 coincides with the first axis 12. The ring gear R2 is provided coaxially with the sun gear S2 on the radially outer side of the sun gear S2. The pinions P2 are arranged between the sun gear S2 and the ring gear R2, and are in mesh with the sun gear S2 and the ring gear R2. The pinions P2 are rotatably supported by the carrier CA2. The carrier CA2 is connected to the ring gear R1 of the transmission unit 40, and rotates integrally with the ring gear R1. Each of the pinions P2 is provided so as to be revolvable about the first axis 12 and rotatable around the central axis of the pinion P2.

The rotary shaft 22 of the first MG 20 is connected to the sun gear S2. The rotary shaft 22 of the first MG 20 rotates integrally with the sun gear S2. The counter drive gear 51 is connected to the ring gear R2. The counter drive gear 51 is an output gear of the differential unit 50. The output gear rotates integrally with the ring gear R2.

As shown in FIG. 6 to FIG. 11 and FIG. 12, the rotation speed of the sun gear S2 (that is, the rotation speed of the first MG 20), the rotation speed of the carrier CA2 and the rotation speed of the ring gear R2 are in the relationship represented by points that are connected by a straight line in each of the nomographs (that is, the relationship that, when any two rotation speeds are determined, the remaining one rotation speed is also determined). Therefore, when the rotation speed of the carrier CA2 is a predetermined value, it is possible to steplessly change the rotation speed of the ring gear R2 by adjusting the rotation speed of the first MG 20.

The counter shaft 70 extends parallel to the first axis 12 and the second axis 14. The counter shaft 70 is arranged parallel to the rotary shaft 22 of the first MG 20 and a rotary shaft 31 of the second MG 30. A driven gear 71 and a drive gear 72 are provided on the counter shaft 70. The driven gear 71 is in mesh with the counter drive gear 51 of the differential unit 50. That is, the power of the engine 10 and the power of the first MG 20 are transmitted to the counter shaft 70 via the counter drive gear 51 of the differential unit 50.

The transmission unit 40 and the differential unit 50 are connected in series with each other in a power transmission path from the engine 10 to the counter shaft 70. Therefore, power from the engine 10 is shifted in the transmission unit 40 and the differential unit 50 and then transmitted to the counter shaft 70.

The driven gear 71 is in mesh with a reduction gear 32 connected to the rotary shaft 31 of the second MG 30. That is, the power of the second MG 30 is transmitted to the counter shaft 70 via the reduction gear 32.

The drive gear 72 is in mesh with a differential ring gear 81 of the differential gear set 80. The differential gear set 80 is connected to the right and left drive wheels 90 via corresponding right and left drive shafts 82. That is, the rotation of the counter shaft 70 is transmitted to the right and left drive shafts 82 via the differential gear set 80.

With the above-described configuration in which the clutch CS is provided, the hybrid vehicle 1 is allowed to operate in a mode in which a series-parallel system is used (hereinafter, referred to as series-parallel mode) and is also allowed to operate in a mode in which a series system is used (hereinafter, referred to as series mode). In terms of this point, how power is transmitted from the engine in each mode will be described with reference to the schematic view shown in FIG. 2.

FIG. 2 is a block diagram that schematically shows power transmission paths of components of the vehicle in FIG. 1. As shown in FIG. 2, the hybrid vehicle 1 includes the engine 10, the first MG 20, the second MG 30, the transmission unit 40, the differential unit 50, a battery 60 and the clutch CS.

The second MG 30 is provided so as to be able to output power to the drive wheels 90. The transmission unit 40 includes the input element and the output element. The power of the engine 10 is input to the input element. The output element outputs the power input to the input element. The transmission unit 40 is configured to be able to switch between the non-neutral state and the neutral state. In the non-neutral state, power is transmitted between the input element and the output element. In the neutral state, power is not transmitted between the input element and the output element.

The battery 60 supplies electric power to the first MG 20 or the second MG 30 during motoring of a corresponding one of the first MG 20 and the second MG 30, and stores electric power generated by the first MG 20 or the second MG 30 during regeneration of a corresponding one of the first MG 20 and the second MG 30.

The differential unit 50 includes a first rotating element, a second rotating element and a third rotating element. The first rotating element is connected to the first MG 20. The second rotating element is connected to the second MG 30 and the drive wheels 90. The third rotating element is connected to the output element of the transmission unit 40. The differential unit 50 is configured as in the case of, for example, the planetary gear mechanism, or the like, such that, when the rotation speeds of any two of the first to third rotating elements are determined, the rotation speed of the remaining one of the first to third rotating elements is determined.

The hybrid vehicle 1 is configured to be able to transmit power from the engine 10 to the first MG 20 with the use of at least any one of two paths K1, K2 through which power is transmitted. The path K1 is a path through which power is transmitted from the engine 10 to the first MG 20 via the transmission unit 40 and the differential unit 50. The path K2 is different from the path K1, and is a path through which power is transmitted from the engine 10 to the first MG 20. The clutch CS is provided in the path K2, and is able to switch between the engaged state and the released state. In the engaged state, power is transmitted from the engine 10 to the first MG 20. In the released state, transmission of power from the engine 10 to the first MG 20 is interrupted.

In HV mode in which the engine is operated, any one of the clutch C1 and the brake B1 is placed in the engaged state, and the other one of the clutch C1 and the brake B1 is placed in the released state. Thus, when the transmission unit 40 is controlled to the non-neutral state, power is transmitted from the engine 10 to the first MG 20 through the path K1. At this time, when the clutch CS is placed in the released state to interrupt the path K2 at the same time, the vehicle is operable in series-parallel mode.

On the other hand, in HV mode in which the engine is operated, when power is transmitted through the path K2 by directly coupling the engine 10 to the first MG 20 with the clutch CS and the path K1 is interrupted by controlling the transmission unit 40 such that the transmission unit 40 is placed in the neutral state by placing both the clutch C1 and the brake B1 in the released state, the vehicle is operable in series mode. At this time, in the differential unit 50, the rotating element connected to the transmission unit 40 is freely rotatable, so the other two rotating elements do not influence each other and are rotatable. Therefore, it is possible to independently perform the operation of generating electric power by rotating the first MG 20 with the use of the rotation of the engine 10 and the operation of rotating the drive wheels by driving the second MG 30 with the use of generated electric power or electric power charged in the battery 60.

The transmission unit 40 does not always need to be able to change the speed ratio. As long as it is possible to interrupt transmission of power between the engine 10 and the differential unit 50 in the path K1, a mere clutch is applicable.

FIG. 3 is a block diagram that shows the configuration of the controller 100 of the vehicle shown in FIG. 1. As shown in FIG. 3, the controller 100 includes an HV ECU 150, an MG ECU 160 and an engine ECU 170. Each of the HV ECU 150, the MG ECU 160 and the engine ECU 170 is an electronic control unit including a computer. The number of ECUs is not limited to three. An integrated single ECU may be provided as a whole, or two or four or more of split ECUs may be provided.

The MG ECU 160 controls the first MG 20 and the second MG 30. The MG ECU 160, for example, controls the output torque of the first MG 20 by adjusting the value of current that is supplied to the first MG 20, and controls the output torque of the second MG 30 by adjusting the value of current that is supplied to the second MG 30.

The engine ECU 170 controls the engine 10. The engine ECU 170, for example, controls the opening degree of an electronic throttle valve of the engine 10, controls ignition of the engine by outputting an ignition signal, or controls injection of fuel to the engine 10. The engine ECU 170 controls the output torque of the engine 10 through opening degree control over the electronic throttle valve, injection control, ignition control, and the like.

The HV ECU 150 comprehensively controls the entire vehicle. A vehicle speed sensor, an accelerator operation amount sensor, an MG1 rotation speed sensor, an MG2 rotation speed sensor, an output shaft rotation speed sensor, a battery sensor, and the like, are connected to the HV ECU 150. With these sensors, the HV ECU 150 acquires a vehicle speed, an accelerator operation amount, the rotation speed of the first MG 20, the rotation speed of the second MG 30, the rotation speed of the output shaft of a power transmission system, a battery state SOC, and the like.

The HV ECU 150 calculates a required driving force, a required power, a required torque, and the like, for the vehicle based on acquired information. The HV ECU 150 determines the output torque of the first MG 20 (hereinafter, also referred to as MG1 torque), the output torque of the second MG 30 (hereinafter, also referred to as MG2 torque) and the output torque of the engine 10 (hereinafter, also referred to as engine torque) based on the calculated required values. The HV ECU 150 outputs a command value of the MG1 torque and a command value of the MG2 torque to the MG ECU 160. The HV ECU 150 outputs a command value of the engine torque to the engine ECU 170.

The HV ECU 150 controls the clutches C1, CS and the brake B1 based on the drive mode (described later), and the like. The HV ECU 150 outputs, to the hydraulic circuit 500 shown in FIG. 1, a command value (PbC1) of hydraulic pressure that is supplied to the clutch C1, a command value (PbCS) of hydraulic pressure that is supplied to the clutch CS and a command value (PbB1) of hydraulic pressure that is supplied to the brake B1. The HV ECU 150 outputs a control signal NM and a control signal S/C to the hydraulic circuit 500 shown in FIG. 1.

The hydraulic circuit 500 shown in FIG. 1 controls hydraulic pressures that are respectively supplied to the clutch C1 and the brake B1 in response to the command values PbC1, PbB1, controls an electric oil pump in response to the control signal NM, and controls whether to allow or prohibit simultaneous engagement of the clutch C1, the brake B1 and the clutch CS in response to the control signal S/C.

Next, the configuration of the hydraulic circuit will be described. FIG. 4 is a view that schematically shows the configuration of the hydraulic circuit 500 mounted on the hybrid vehicle 1. The hydraulic circuit 500 includes a mechanical oil pump (hereinafter, also referred to as MOP) 501, the electric oil pump (hereinafter, also referred to as EOP) 502, pressure regulating valves 510, 520, linear solenoid valves SL1, SL2, SL3, simultaneous supply prevention valves 530, 540, 550, an electromagnetic change-over valve 560, a check valve 570, and oil passages LM, LE, L1, L2, L3, L4.

The MOP 501 is driven by the rotation of the carrier CA2 of the differential unit 50 to generate hydraulic pressure. Therefore, when the carrier CA2 is rotated by, for example, driving the engine 10, the MOP 501 is also driven; whereas, when the carrier CA2 is stopped, the MOP 501 is also stopped. The MOP 501 outputs generated hydraulic pressure to the oil passage LM.

The hydraulic pressure in the oil passage LM is regulated (reduced) to a predetermined pressure by the pressure regulating valve 510. Hereinafter, the hydraulic pressure in the oil passage LM, regulated by the pressure regulating valve 510, is also referred to as line pressure PL. The line pressure PL is supplied to each of the linear solenoid valves SL1, SL2, SL3.

The linear solenoid valve SL1 generates hydraulic pressure for engaging the clutch C1 (hereinafter, referred to as C1 pressure) by regulating the line pressure PL in response to the hydraulic pressure command value PbC1 from the controller 100. The C1 pressure is supplied to the clutch C1 via the oil passage L1.

The linear solenoid valve SL2 generates hydraulic pressure for engaging the brake B1 (hereinafter, referred to as B1 pressure) by regulating the line pressure PL in response to the hydraulic pressure command value PbB1 from the controller 100. The B1 pressure is supplied to the brake B1 via the oil passage L2.

The linear solenoid valve SL3 generates hydraulic pressure for engaging the clutch CS (hereinafter, referred to as CS pressure) by regulating the line pressure PL in response to the hydraulic pressure command value PbCS from the controller 100. The CS pressure is supplied to the clutch. CS via the oil passage L3.

The simultaneous supply prevention valve 530 is provided in the oil passage L1, and is configured to prevent the clutch C1 and at least one of the brake B1 and the clutch CS from being simultaneously engaged. Specifically, the oil passages L2, L3 are connected to the simultaneous supply prevention valve 530. The simultaneous supply prevention valve 530 operates by using the B1 pressure and the CS pressure through the oil passages L2, L3 as signal pressures.

When both signal pressures that are the B1 pressure and the CS pressure are not input to the simultaneous supply prevention valve 530 (that is, when both the brake B1 and the clutch CS are released), the simultaneous supply prevention valve 530 is in a normal state in which the C1 pressure is supplied to the clutch C1. FIG. 4 illustrates the case where the simultaneous supply prevention valve 530 is in the normal state.

On the other hand, when at least one of the signal pressures that are the B1 pressure and the CS pressure is input to the simultaneous supply prevention valve 530 (that is, when at least one of the brake B1 and the clutch CS is engaged), even when the clutch C1 is engaged, the simultaneous supply prevention valve 530 switches into a drain state in which supply of the C1 pressure to the clutch C1 is cut off and the hydraulic pressure in the clutch C1 is released to the outside. Thus, the clutch C1 is released, so the clutch C1 and at least one of the brake B1 and the clutch CS are prevented from being simultaneously engaged.

Similarly, the simultaneous supply prevention valve 540 operates in response to the C1 pressure and the CS pressure as signal pressures to prevent the brake B1 and at least one of the clutch C1 and the clutch CS from being simultaneously engaged. Specifically, when both the signal pressures that are the C1 pressure and the CS pressure are not input to the simultaneous supply prevention valve 540, the simultaneous supply prevention valve 540 is in a normal state in which the B1 pressure is supplied to the brake B1. On the other hand, when at least one of the signal pressures that are the C1 pressure and the CS pressure is input to the simultaneous supply prevention valve 540, the simultaneous supply prevention valve 540 switches into a drain state in which supply of the B1 pressure to the brake B1 is cut off and the hydraulic pressure in the brake B1 is released to the outside. FIG. 4 illustrates the case where the C1 pressure is input to the simultaneous supply prevention valve 540 as the signal pressure and the simultaneous supply prevention valve 540 is in the drain state.

Similarly, the simultaneous supply prevention valve 550 operates by using the C1 pressure and the B1 pressure as signal pressures to prevent the clutch CS and at least one of the clutch C1 and the brake B1 from being simultaneously engaged. Specifically, when both the signal pressures that are the C1 pressure and the B1 pressure are not input to the simultaneous supply prevention valve 550, the simultaneous supply prevention valve 550 is in a normal state in which the CS pressure is supplied to the clutch CS. On the other hand, when at least one of the signal pressures that are the C1 pressure and the B1 pressure is input to the simultaneous supply prevention valve 550, the simultaneous supply prevention valve 550 switches into a drain state in which supply of the CS pressure to the clutch CS is cut off and the hydraulic pressure in the clutch CS is released to the outside. FIG. 4 illustrates the case where the C1 pressure is input to the simultaneous supply prevention valve 550 and the simultaneous supply prevention valve 550 is in the drain state.

The EOP 502 is driven by a motor (hereinafter, also referred to as internal motor) 502A provided inside to generate hydraulic pressure. The internal motor 502A is controlled by the control signal NM from the controller 100. Therefore, the EOP 502 is operable irrespective of whether the carrier CA2 is rotating. The EOP 502 outputs generated hydraulic pressure to the oil passage LE.

The hydraulic pressure in the oil passage LE is regulated (reduced) to a predetermined pressure by the pressure regulating valve 520. The oil passage LE is connected to the oil passage LM via the check valve 570. When the hydraulic pressure in the oil passage LE is higher by a predetermined pressure or more than the hydraulic pressure in the oil passage LM, the check valve 570 opens, and the hydraulic pressure in the oil passage LE is supplied to the oil passage LM via the check valve 570. Thus, during a stop of the MOP 501 as well, it is possible to supply hydraulic pressure to the oil passage LM by driving the EOP 502.

The electromagnetic change-over valve 560 is switched to any one of an on state and an off state in response to the control signal S/C from the controller 100. In the on state, the electromagnetic change-over valve 560 communicates the oil passage LE with the oil passage L4. In the off state, the electromagnetic change-over valve 560 interrupts the oil passage LE from the oil passage L4, and releases the hydraulic pressure in the oil passage L4 to the outside. FIG. 4 illustrates the case where the electromagnetic change-over valve 560 is in the off state.

The oil passage L4 is connected to the simultaneous supply prevention valves 530, 540. When the electromagnetic change-over valve 560 is in the on state, the hydraulic pressure in the oil passage LE is input to the simultaneous supply prevention valves 530, 540 via the oil passage L4 as a signal pressure. When the signal pressure from the oil passage L4 is input to the simultaneous supply prevention valve 530, the simultaneous supply prevention valve 530 is forcibly fixed to the normal state irrespective of whether the signal pressure (B1 pressure) is input from the oil passage L2. Similarly, when the signal pressure is input from the oil passage L4 to the simultaneous supply prevention valve 540, the simultaneous supply prevention valve 540 is forcibly fixed to the normal state irrespective of whether the signal pressure (C1 pressure) is input from the oil passage L1. Therefore, by driving the EOP 502 and switching the electromagnetic change-over valve 560 to the on state, the simultaneous supply prevention valves 530, 540 are simultaneously fixed to the normal state. Thus, the clutch C1 and the brake B1 are allowed to be simultaneously engaged, and two-motor mode (described later) is enabled.

Hereinafter, the details of control modes of the hybrid vehicle 1 will be described with reference to an operation engagement chart and the nomographs.

FIG. 5 is a chart that shows each drive mode and controlled statuses of the clutch C1 and brake B1 of the transmission unit 40 in each drive mode.

The controller 100 causes the hybrid vehicle 1 to travel in motor drive mode (hereinafter, referred to as EV mode) or hybrid mode (hereinafter, referred to as HV mode). The EV mode is a control mode in which the engine 10 is stopped and the hybrid vehicle 1 is caused to travel by using the power of at least one of the first MG 20 and the second MG 30. The HV mode is a control mode in which the hybrid vehicle 1 is caused to travel by using the power of the engine 10 and the power of the second MG 30. Each of the EV mode and the HV mode is further divided into some control modes.

In FIG. 5, C1, B1, CS, MG1 and MG2 respectively denote the clutch C1, the brake B1, the clutch CS, the first MG 20 and the second MG 30. The circle mark (◯) in each of the C1, B1, CS columns indicates the engaged state, the cross mark (x) indicates the released state, and the triangle mark (Δ) indicates that any one of the clutch C1 and the brake B1 is engaged during engine brake. The sign G in each of the MG1 column and the MG2 column indicates that the MG1 or the MG2 is mainly operated as a generator. The sign M in each of the MG1 column and the MG2 column indicates that the MG1 or the MG2 is mainly operated as a motor.

In EV mode, the controller 100 selectively switches between one-motor mode and two-motor mode in response to a user's required torque, and the like. In one-motor mode, the hybrid vehicle 1 is caused to travel by using the power of the second MG 30 alone. In two-motor mode, the hybrid vehicle 1 is caused to travel by using the power of both the first MG 20 and the second MG 30.

When the load of the drive system 2 is low, the one-motor mode is used. When the load of the drive system 2 becomes high, the drive mode is changed to the two-motor mode.

As shown in E1 line of FIG. 5, when the hybrid vehicle 1 is driven (moved forward or reversed) in one-motor EV mode, the controller 100 places the transmission unit 40 in the neutral state (state in which no power is transmitted) by releasing the clutch C1 and releasing the brake B1. At this time, the controller 100 causes the first MG 20 to mainly operate as fixing means for fixing the rotation speed of the sun gear S2 to zero and causes the second MG 30 to mainly operate as a motor (see FIG. 6 (described later)). In order to cause the first MG 20 to operate as the fixing means, the current of the first MG 20 may be controlled by feeding back the rotation speed of the first MG 20 such that the rotation speed becomes zero. When the rotation speed of the first MG 20 is kept zero even when torque is zero, cogging torque may be utilized without adding current. When the transmission unit 40 is placed in the neutral state, the engine 10 is not co-rotated during braking, so a loss is smaller by that amount, and it is possible to recover large regenerated electric power.

As shown in E2 line in FIG. 5, when the hybrid vehicle 1 is braked in one-motor EV mode and engine brake is required, the controller 100 engages any one of the clutch C1 and the brake B1. For example, when braking force is insufficient with only regenerative brake, engine brake is used together with regenerative brake. For example, when the SOC of the battery 60 is close to a full charge state, regenerated electric power cannot be charged, so it is conceivable to establish an engine brake state.

By engaging any one of the clutch C1 and the brake B1, a so-called engine brake state is established. In the engine brake state, the rotation of the drive wheels 90 is transmitted to the engine 10, and the engine 10 is rotated. At this time, the controller 100 causes the first MG 20 to mainly operate as a motor, and causes the second MG 30 to mainly operate as a generator.

On the other hand, as shown in the E3 line in FIG. 5, when the hybrid vehicle 1 is driven (moved forward or reversed) in two-motor EV mode, the controller 100 restricts (locks) the rotation of the ring gear R1 of the transmission unit 40 by engaging the clutch C1 and engaging the brake B1. Thus, the rotation of the carrier CA2 of the differential unit 50 coupled to the ring gear R1 of the transmission unit 40 is also restricted (locked), so the carrier CA2 of, the differential unit 50 is kept in a stopped state (Engine Rotation Speed Ne=0). The controller 100 causes the first MG 20 and the second MG 30 to mainly operate as motors (see FIG. 7 (described later)).

In EV mode (one-motor mode or two-motor mode), the engine 10 is stopped, so the MOP 501 is also stopped. Therefore, in EV mode, the clutch C1 or the brake B1 is engaged by using hydraulic pressure that is generated by the EOP 502.

In HV mode, the controller 100 causes the first MG 20 to mainly operate as a generator, and causes the second MG 30 to mainly operate as a motor.

In HV mode, the controller 100 sets the control mode to any one of the series-parallel mode and the series mode.

In series-parallel mode, part of the power of the engine 10 is used in order to drive the drive wheels 90, and the remaining part of the power of the engine 10 is used as power for generating electric power in the first MG 20. The second MG 30 drives the drive wheels 90 by using electric power generated by the first MG 20. In series-parallel mode, the controller 100 changes the speed ratio of the transmission unit 40 in response to the vehicle speed.

When the hybrid vehicle 1 is caused to move forward in an intermediate or low speed range, the controller 100 establishes the low gear position Lo (see the continuous line in FIG. 8 (described later)) by engaging the clutch C1 and releasing the brake B1 as shown in the H2 line in FIG. 5. On the other hand, when the hybrid vehicle 1 is caused to move forward in a high speed range, the controller 100 establishes the high gear position Hi (see the dashed line in FIG. 8 (described later)) by releasing the clutch C1 and engaging the brake B1 as shown in the H1 line in FIG. 5. Either when the high gear position is established or when the low gear position is established, the transmission unit 40 and the differential unit 50 operate as a continuously variable transmission as a whole.

When the hybrid vehicle 1 is reversed, the controller 100 engages the clutch C1 and releases the brake B1 as shown in the H3 line in FIG. 5. When there is an allowance in the SOC of the battery, the controller 100 rotates the second MG 30 alone in the reverse direction; whereas, when there is no allowance in the SOC of the battery, the controller 100 generates electric power with the use of the first MG 20 by operating the engine 10 and rotates the second MG 30 in the reverse direction.

In series mode, the entire power of the engine 10 is used as power for generating electric power with the use of the first MG 20. The second. MG 30 drives the drive wheels 90 by using electric power generated by the first MG 20. In series mode, when the hybrid vehicle 1 is moved forward or when the hybrid vehicle 1 is reversed, the controller 100 releases both the clutch C1 and the brake B1 and engages the clutch CS (see FIG. 9 (described later)) as shown in the H4 line and the H5 line in FIG. 5.

In HV mode, the engine 10 is operating, so the MOP 501 is also operating. Therefore, in HV mode, the clutch C1, the clutch CS or the brake B1 is engaged mainly by using hydraulic pressure generated by the MOP 501.

Hereinafter, the statuses of the rotating elements in each operation mode shown in FIG. 5 will be described with reference to the nomographs.

FIG. 6 is a nomograph in one-motor EV mode. FIG. 7 is a nomograph in two-motor EV mode. FIG. 8 is a nomograph in series-parallel mode. FIG. 9 is a nomograph in series mode.

In FIG. 6 to FIG. 9, S1, CA1 and R1 respectively denote the sun gear 51, the carrier CA1 and the ring gear R1 of the transmission unit 40, S2, CA2 and R2 respectively denote the sun gear S2, the carrier CA2 and the ring gear R2 of the differential unit 50.

The controlled statuses in one-motor EV mode (E1 line in FIG. 5) will be described with reference to FIG. 6. In one-motor EV mode, the controller 100 releases the clutch C1 and brake B1 of the transmission unit 40 and the clutch CS, stops the engine 10, and causes the second MG 30 to mainly operate as a motor. Therefore, in one-motor EV mode, the hybrid vehicle 1 travels by using the torque of the second MG 30 (hereinafter, referred to as MG2 torque Tm2).

At this time, the controller 100 executes feedback control over the torque of the first MG 20 (hereinafter, referred to as MG1 torque Tm1) such that the rotation speed of the sun gear S2 becomes zero. Therefore, the sun gear S2 does not rotate. However, because the clutch C1 and brake B1 of the transmission unit 40 are released, the rotation of the carrier CA2 of the differential unit 50 is not restricted. Therefore, the ring gear R2 and carrier CA2 of the differential unit 50 and the ring gear R1 of the transmission unit 40 are rotated (coasted) interlocking with the rotation of the second MG 30 in the same direction as the second MG 30.

On the other hand, the carrier CA1 of the transmission unit 40 is kept in a stopped state because the engine 10 is stopped. The sun gear S1 of the transmission unit 40 is rotated (coasted) interlocking with the rotation of the ring gear R1 in a direction opposite to the rotation direction of the ring gear R1.

In order to decelerate the vehicle in one-motor EV mode, it is allowed to activate engine brake in addition to regenerative brake using the second MG 30. In this case (E2 line in FIG. 5), by engaging any one of the clutch C1 and the brake B1, the engine 10 is also rotated at the time when the carrier CA2 is driven from the drive wheels 90 side, so engine brake is activated.

Next, the controlled status in two-motor EV mode (E3 line in FIG. 5) will be described with reference to FIG. 7. In two-motor EV mode, the controller 100 engages the clutch C1 and the brake B1, releases the clutch CS, and stops the engine 10. Therefore, the rotation of each of the sun gear S1, carrier CA1 and ring gear R1 of the transmission unit 40 is restricted such that the rotation speed becomes zero.

Because the rotation of the ring gear R1 of the transmission unit 40 is restricted, the rotation of the carrier CA2 of the differential unit 50 is also restricted (locked). In this state, the controller 100 causes the first MG 20 and the second MG 30 to mainly operate as motors. Specifically, the second MG 30 is rotated in the positive direction by setting the MG2 torque Tm2 to a positive torque, and the first MG 20 is rotated in the negative direction by setting the MG1 torque Tm1 to a negative torque.

When the rotation of the carrier CA2 is restricted by engaging the clutch C1, the MG1 torque Tint is transmitted to the ring gear R2 by using the carrier CA2 as a supporting point. The MG1 torque Tm1 (hereinafter, referred to as MG1 transmission torque Tm1 c) that is transmitted to the ring gear R2 acts in the positive direction, and is transmitted to the counter shaft 70. Therefore, in two-motor EV mode, the hybrid vehicle 1 travels by using the MG1 transmission torque Tm1 c and the MG2 torque Tm2. The controller 100 adjusts the distribution ratio between the MG1 torque Tm1 and the MG2 torque Tm2 such that the sum of the MG1 transmission torque Tm1 c and the MG2 torque Tm2 meets the user's required torque.

The controlled state in series-parallel HV mode (H1 to H3 lines in FIG. 5) will be described with reference to FIG. 8. FIG. 8 illustrates the case where the vehicle is traveling forward in the low gear position Lo (see H2 line in FIG. 5, and the continuous common line shown in the nomograph of S1, CA1 and R1 in FIG. 8) and the case where the vehicle is traveling forward in the high gear position Hi (see H1 line in FIG. 5, and the dashed common line shown in the nomograph of S1, CA1 and R1 in FIG. 8). For the sake of convenience of description, it is assumed that the rotation speed of the ring gear R1 is the same either when the vehicle is traveling forward in the low gear position Lo or when the vehicle is traveling forward in the high gear position Hi.

When the low gear position Lo is established in series-parallel HV mode, the controller 100 engages the clutch C1, and releases the brake B1 and the clutch CS. Therefore, the rotating elements (the sun gear S1, the carrier CA1 and the ring gear R1) rotate integrally with one another. Thus, the ring gear R1 of the transmission unit 40 also rotates at the same rotation speed as the carrier CA1, and the rotation of the engine 10 is transmitted from the ring gear R1 to the carrier CA2 of the differential unit 50 at the same rotation speed. That is, the torque of the engine 10 (hereinafter, referred to as engine torque Te) input to the carrier CA1 of the transmission unit 40 is transmitted from the ring gear R1 of the transmission unit 40 to the carrier CA2 of the differential unit 50. When the low gear position Lo is established, the torque that is transmitted from the ring gear R1 (hereinafter, referred to as transmission unit output torque Tr1) is equal to the engine torque Te (Te=Tr1).

The rotation of the engine 10, transmitted to the carrier CA2 of the differential unit 50, is steplessly shifted by the use of the rotation speed of the sun gear S2 (the rotation speed of the first MG 20), and is transmitted to the ring gear R2 of the differential unit 50. At this time, the controller 100 basically causes the first MG 20 to operate as a generator to apply the MG1 torque Tm1 in the negative direction. Thus, the MG1 torque Tm1 serves as reaction force for transmitting the engine torque Te, input to the carrier CA2, to the ring gear R2.

The engine torque Te transmitted to the ring gear R2 (hereinafter, referred to as engine transmission torque Tec) is transmitted from the counter drive gear 51 to the counter shaft 70, and acts as driving force of the hybrid vehicle 1.

In series-parallel HV mode, the controller 100 causes the second MG 30 to mainly operate as a motor. The second MG torque Tm2 is transmitted from the reduction gear 32 to the counter shaft 70, and acts as driving force of the hybrid vehicle 1. That is, in series-parallel HV mode, the hybrid vehicle 1 travels by using the engine transmission torque Tec and the second MG torque Tm2.

On the other hand, when the high gear position Hi is established in series-parallel HV mode, the controller 100 engages the brake B1, and releases the clutch C1 and the clutch CS. Because the brake B1 is engaged, the rotation of the sun gear S1 is restricted. Thus, the rotation of the engine 10, input to the carrier CA1 of the transmission unit 40, is increased in speed, and is transmitted from the ring gear R1 of the transmission unit 40 to the carrier CA2 of the differential unit 50. Therefore, when the high gear position Hi is established, the transmission unit output torque Tr1 is smaller than the engine torque Te (Te>Tr1).

The controlled status in series HV mode (H4 line in FIG. 5) will be described with reference to FIG. 9. In series HV mode, the controller 100 releases the clutch C1 and the brake B1, and engages the clutch CS. Therefore, when the clutch CS is engaged, the sun gear S2 of the differential unit 50 rotates at the same rotation speed as the carrier CA1 of the transmission unit 40, and the rotation of the engine 10 is transmitted from the clutch CS to the first MG 20 at the same rotation speed. Thus, electric power is allowed to be generated with the use of the first MG 20 by using the engine 10 as a power source.

On the other hand, because both the clutch C1 and the brake B1 are released, the rotation of each of the sun gear S1 and ring gear R1 of the transmission unit 40 and the rotation of the carrier CA2 of the differential unit 50 are not restricted. That is, because the transmission unit 40 is in the neutral state and the rotation of the carrier CA2 of the differential unit 50 is not restricted, the power of the first MG 20 and the power of the engine 10 are not transmitted to the counter shaft 70. Therefore, the MG2 torque Tm2 of the second MG 30 is transmitted to the counter shaft 70. Therefore, in series HV mode, while electric power is generated with the use of the first MG 20 by using the engine 10 as a power source, the hybrid vehicle 1 travels by using the MG2 torque Tm2 with the use of part or all of the generated electric power.

Because the series mode is allowed to be achieved, it is possible to select the operating point of the engine without concern for occurrence of tooth contact noise of the gear mechanism due to engine torque fluctuations, to which attention needs to be paid in series-parallel mode, when the vehicle travels at a low vehicle speed or when the vehicle is in a vehicle state where background noise is low. Thus, a vehicle state that enables both quietness of the vehicle and improvement in fuel consumption increases.

As described in the control modes shown in FIG. 5, when the engine 10 and the first MG 20 are directly coupled to each other with the clutch CS and the transmission unit 40 is controlled to the neutral state by placing both the clutch C1 and the brake B1 in the released state in HV mode, the vehicle is operable in series mode.

Hereinafter, the fact that it is possible to cause the vehicle to operate in further another operation mode with the use of the clutch CS will be described.

FIG. 10 is a chart that shows controlled statuses of the clutch C1 and brake B1 of the transmission unit 40 in each drive mode according to an alternative embodiment to the present embodiment.

In FIG. 10, E4 and E5 lines are added to the EV mode in FIG. 5, and H6 to H9 lines are added to the HV mode in FIG. 5. The marks in FIG. 10 denote similar meanings to the marks in FIG. 5.

Initially, E4 and E5 lines added to the EV mode will be described. These additional modes as well as E3 line are two-motor modes, and differ from E3 line in that these additional modes are operable even when the engine rotation speed Ne is not zero (Ne free in FIG. 10).

FIG. 11 is a nomograph for illustrating the operations of E4 and E5 lines in FIG. 10. The controlled statuses in two-motor EV mode will be described with reference to FIG. 11. FIG. 11 illustrates the case where the vehicle is traveling forward in the low gear position Lo (see the continuous common lines shown in FIG. 11) and the case where the vehicle is traveling in the high gear position Hi (see the dashed common lines shown in FIG. 11). For the sake of convenience of description, it is assumed that the rotation speed of the ring gear R1 is the same either when the vehicle is traveling forward in the low gear position Lo or when the vehicle is traveling forward in the high gear position Hi.

When the low gear position Lo is established in two-motor EV mode (E5 line in FIG. 10), the controller 100 engages the clutch C1 and the clutch CS and releases the brake B1. Therefore, the rotating elements (the sun gear S1, the carrier CA1 and the ring gear R1) of the transmission unit 40 rotate integrally with one another. When the clutch CS is engaged, the carrier CA1 of the transmission unit 40 and the sun gear S2 of the differential unit 50 rotate integrally with each other. Thus, all the rotating elements of the transmission unit 40 and differential unit 50 rotate integrally at the same rotation speed. Therefore, when the MG1 torque Tm1 is generated in the positive rotation direction by the first MG 20 together with the second MG 30, it is possible to cause the hybrid vehicle 1 to travel by using both the motors. Because the engine 10 is not autonomously driven in EV mode, the engine 10 is in a driven state where the engine 10 is driven by the torque of both the first MG 20 and the second MG 30. Therefore, it is desirable that the open/close timing of each valve be operated such that resistance during rotation of the engine reduces.

The MG1 transmission torque Tm1 c transmitted to the ring gear R2 is transmitted from the counter drive gear 51 to the counter shaft 70, and acts as the driving force of the hybrid vehicle 1. At the same time, the MG2 torque Tm2 is transmitted from the reduction gear 32 to the counter shaft 70, and acts as the driving force of the hybrid vehicle 1. That is, when the low gear position Lo is established in two-motor EV mode, the hybrid vehicle 1 travels by using the MG2 torque Tm2 and the MG1 torque Tm1 transmitted to the ring gear R2.

On the other hand, when the high gear position Hi is established in two-motor EV mode (E4 line in FIG. 10), the controller 100 engages the brake B1 and the clutch CS and releases the clutch C1. Because the brake B1 is engaged, the rotation of the sun gear S1 is restricted.

When the clutch CS is engaged, the carrier CA1 of the transmission unit 40 and the sun gear S2 of the differential unit 50 rotate integrally with each other. Therefore, the rotation speed of the sun gear S2 is equal to the rotation speed of the engine 10.

FIG. 12 is a nomograph for illustrating the operations of H6 to H9 lines in FIG. 10. The controlled statuses in two-motor HV mode (parallel mode: stepped) will be described with reference to FIG. 12. FIG. 12 illustrates the case where the vehicle is traveling forward in the low gear position Lo (see the continuous common lines shown in FIG. 12) and the case where the vehicle is traveling in the high gear position Hi (see the dashed common lines shown in FIG. 12).

As is apparent from the comparison between FIG. 11 and FIG. 12, in two-motor HV mode (parallel mode: stepped), the engine 10 is autonomously driven, so the engine torque Te is applied to the carrier CA1 shown in FIG. 12. Therefore, the engine torque Te is also added to the ring gear R2. The remaining points of the nomograph shown in FIG. 12 are the same as those of FIG. 11, so the description will not be repeated.

In two-motor HV mode (parallel mode: stepped), the engine torque Te, the MG1 torque Tm1 and the MG2 torque Tm2 all are allowed to be used for the forward rotation torque of the drive wheels, so it is particularly effective when a large torque is required of the drive wheels.

The controlled statuses in one-motor HV mode (parallel mode: stepped) corresponds to the case where Tm1=0 in FIG. 12. In HV mode (parallel mode: stepped), the hybrid vehicle 1 is able to travel by using only the engine torque in a state where Tm1=0 and Tm2=0.

Next, engine startup control at the time of shifting from the EV mode to the HV mode will be described. As described above, the hybrid vehicle 1 is able to select any one of the series-parallel HV mode and the series HV mode while traveling in HV mode.

In series HV mode, because the transmission unit 40 is in the neutral state, the engine 10 is separated from the drive wheels. Thus, at the time of starting the engine, a startup shock of the engine is difficult to reach a vehicle body. However, if the drive mode always shifts into the series-parallel HV mode via the series HV mode at a startup of the engine, it is disadvantageous in terms of the response of the vehicle, causing a driver to experience a feeling of slowness.

In the present embodiment, at the time of starting the engine 10, control at the time of starting the engine 10 is switched in consideration of the condition of the vehicle and driver's taste. Hereinafter, the engine startup control will be described with reference to the flowchart, and the like.

FIG. 13 is a flowchart that shows the details of a first example of engine startup control that is executed by the controller 100. As shown in FIG. 13, when the process of the flowchart is started, it is initially determined in step S10 whether an engine startup request has been issued.

For example, when the SOC of the battery 60 becomes lower than a lower limit threshold or when a driver requires acceleration by increasing the depression amount of an accelerator pedal, an engine startup request is issued. When no engine startup request has been issued and the EV mode is continued (NO in S10), the process proceeds to step S80, and exits from control of the flowchart.

When it is determined in step S10 that an engine startup request has been issued (YES in S10), the process proceeds to step S20. In step S20, it is determined which mode is the operation mode after an engine startup. A mode determination map is used in this determination.

FIG. 14 is a graph that shows an example of the mode determination map that is used in step S20. FIG. 14 overlappingly shows a map of which boundary lines are indicated by dashed lines and a map of which boundary lines are indicated by continuous lines. The map of which the boundary lines are indicated by dashed lines is a map that is ordinarily used when the input/output power of the battery 60 is not limited. On the other hand, the map of which the boundary lines are indicated by continuous lines is a map that is used when the input/output power of the battery 60 is limited depending on some conditions, such as the SOC and the temperature.

Initially, a region in which a vehicle load is positive in the map of which the boundary lines are indicated by dashed lines will be described. In a region in which a vehicle speed is close to zero and the vehicle load is small, the one-motor EV mode is used. The reason why the drive mode is not the two-motor mode but the one-motor mode is to make it possible to start the engine immediately at the time of sudden depression of the accelerator pedal. When the vehicle speed is high or the vehicle load is large; the series-parallel HV mode (Lo gear) is used. When the vehicle load further increases and torque becomes insufficient in series-parallel HV mode, all the engine torque is output to the drive wheels in parallel mode (Lo gear), and motor assist using the MG1 torque or the MG2 torque is performed. This mode may be used at the time of a power-on downshift.

Subsequently, a region in which the vehicle load is negative in the map of which the boundary lines are indicated by dashed lines will be described. In a region in which the vehicle speed is close to zero and the vehicle load is small, the one-motor EV mode is used. When the vehicle speed increases, the series HV mode is used. The reason why the region of the one-motor EV mode is wider when the vehicle load is negative than when the vehicle load is positive is because the engine is started in series mode and, therefore, an allowance for the amount of reaction torque for reducing a shock at an engine startup does not need to be provided.

Next, the region in which the vehicle load is positive in the map of which the boundary lines are indicated by continuous lines will be described. When the vehicle load is positive and the vehicle speed is low, the series HV mode is performed. The series HV mode is an operation mode that is effective to prevent noise (so-called rattle) due to rattling between the second MG 30 and the differential gear set.

With an increase in the vehicle speed, the operation mode shifts from the series mode to the parallel mode (Hi gear) in which no motor assist is used and then to the series-parallel HV mode (Hi gear). Because the parallel mode (Hi gear) has a fixed gear ratio, the engine 10 tends to deviate from the operating point that minimizes fuel consumption, so a service region has a relatively narrow band shape.

When the vehicle load increases, the operation mode shifts from the series mode to the series-parallel mode (Lo). The series-parallel mode (Lo) is an effective operation mode in a region in which driving force is given a higher priority.

Next, the region in which the vehicle load is negative in the map of which the boundary lines are indicated by continuous lines will be described. When the vehicle load is negative, the series mode is used irrespective of the vehicle speed. In series mode, the engine rotation speed is arbitrarily controllable at the same vehicle speed, so it is possible to generate engine brake torque commensurate with a driver's request. Because the first MG 20 is rotated against the engine brake torque, the first MG 20 performs motoring operation. Therefore, regenerated electric power generated by regenerative brake in the second MG 30 is allowed to be consumed by the first MG 20, so, even when the battery 60 cannot receive regenerated electric power, it is possible to perform regenerative brake with the use of the second MG 30. In addition, because the rotation speed of the first MG 20 is equal to the engine rotation speed, the series mode is insusceptible to constraints of the engine rotation speed due to the upper limit of the rotation speed of the first MG 20 as compared to the other modes, so it is possible to increase the absolute value of the engine brake torque.

Referring back to FIG. 13, when the operation mode is not the series mode in step S20 (NO in S20), the process proceeds to step S30; whereas, when the operation mode is the series mode (YES in S20), the process proceeds to step S60.

In step S30, it is determined whether the vehicle is stopped. When the vehicle is stopped, a driver easily experiences vibrations, so it is desirable that the engine should be started in a state where the engine is separated from the drive wheels. Therefore, when it is determined in step S30 that the vehicle is stopped (YES in S30), the process proceeds to step S60. On the other hand, when it is determined in step S30 that the vehicle is not stopped (NO in S30), the process proceeds to step S40.

In step S40, it is determined whether the mode selected by a user with the use of a mode switch 180 is a comfort mode or an economy mode. When any one of these modes is selected, it is presumable that the user prefers reducing a shock of an engine startup to increasing the response of the vehicle. When it is determined in step S40 that the comfort mode or the economy mode is selected (YES in step S40), the process proceeds to step S60; whereas, when it is determined that none of these modes is not selected (NO in step S40), the process proceeds to step S50.

When the mode selected by the user with the use of the mode switch 180 is a sport mode or a power mode in step S40, the process may proceed to step S50; otherwise, the process may proceed to step S60.

In step S50, the clutch C1 is engaged, and the first startup method for starting the engine is executed. At this time, instead of the clutch C1, the brake B1 may be engaged. In this first startup method, acceleration response is high; however, an engine startup shock is easily transmitted to the drive wheels.

On the other hand, when the process proceeds to step S60, the second startup method by which an engine startup shock is reduced is executed. Initially, in step S60, the transmission unit 40 is set to the neutral state. Subsequently, in step S70, the clutch CS is engaged, and the engine 10 is started with the use of the first MG 20. In series mode, the transmission unit 40 is placed in the neutral state, so the path K1 shown in FIG. 2 is interrupted. Therefore, vibrations at a startup of the engine 10 are difficult to be transmitted to the drive wheels 90, so an engine startup shock that is experienced by a user is reduced.

FIG. 15 is an operation waveform chart that shows an example of an engine startup of the hybrid vehicle. As shown in FIG. 15, in an initial state at time to, the hybrid vehicle is traveling in one-motor EV mode. A positive torque and a positive rotation speed are output from the second MG 30. The torque and rotation speed of the first MG 20 are zero. An engine torque and an engine rotation speed are zero, so the engine 10 is not in operation.

In one-motor EV mode, the engine rotation speed is zero, so the hybrid vehicle is able to travel in any state where the clutch C1 and the brake B1 each are engaged or released. However, for the purpose of reducing an energy loss as much as possible, both the C1 pressure and the B1 pressure are set to zero, and both the clutch C1 and the brake B1 are released.

At time t2, the SOC gradually reduces and, as a result, the SOC reaches a lower limit value, and a determination of a startup of the engine 10 for charging the battery 60 is finalized (YES in step S20). Accordingly, at time t2, an increase in the CS pressure is started. At this time, both the rotation speeds of the rotating elements (CA1 and S2) of the clutch CS are zero as shown in FIG. 6, and differential rotation is zero, so a shock is small even without spending time on engagement. At time t2, an engine startup time is shortened by steeply raising hydraulic pressure to some extent.

At time t3, because the CS pressure has sufficiently risen, the first MG 20 is caused to generate MG1 torque, and the rotation speed of the first MG 20 is increased from zero, thus initiating a startup of the engine 10. At time t4, the engine is ignited at the timing at which the engine rotation speed has reached about 600 rpm, and the engine torque increases from time t4 to time t5.

At time t6, in response to the fact that the engine 10 is able to stably generate torque, the MG1 torque of the first MG 20 is set to a negative value. This means that, at time t6, the first MG 20 starts generating electric power by using the engine torque. The amount of electric power that is generated by the first MG 20 at this time is set so as to be larger than the amount of electric power that is consumed by the second MG 30. Therefore, the SOC of the battery 60 rises from time t6 to time t7.

FIG. 16 is a flowchart that shows the details of a second example of engine startup control that is executed by the controller 100. The flowchart shown in FIG. 16 differs from the flowchart shown in FIG. 13 in that the process of step S20 in the flowchart shown in FIG. 13 is replaced with step S20A. The other steps of FIG. 16 are the same as those of FIG. 13, so the description will not be repeated.

In step S20, the engine startup method is selected based on which mode is the operation mode after an engine startup. Instead, in step S20A, in EV mode before an engine startup, it is determined whether the rotation speed (hereinafter, referred to as N(CA2)) of the carrier CA2 of the differential unit 50 is higher than a predetermined value Nth close to zero. When N(CA2) is higher than Nth in step S20A (YES in step S20A), the process proceeds to step S60; whereas, when N(CA2) is not higher than Nth (NO in step S20A), the process proceeds to step S30.

It may be determined in step S20 whether the rotation speed (hereinafter, referred to as Ng) of the first MG 20 is close to zero, the process may proceed to step S60 when Ng is almost equal to zero in step S20A (YES in step S20A), and the process may proceed to step S30 when Ng is not almost equal to zero (NO in step S20A).

The reason why the startup method is selected in this way is to shorten a time that is required to start the engine. This will be described by showing a difference in steps in the case where the engine is started in accordance with the two engine startup methods in a state before an engine startup.

FIG. 17 is a table for illustrating the correspondence relationship between a pre-engine startup state and an engine startup state. In the case shown in K1 line, the pre-engine startup state (in EV mode) is the one-motor mode, N(CA2) is almost equal to zero and Ng is lower than 0. In the case shown in K2 line, the pre-engine startup state (in EV mode) is the one-motor mode and N(CA2) is not equal to zero and Ng is almost equal to zero. In the case shown in K3 line, the pre-engine startup state (in EV mode) is the two-motor mode, and Ng is lower than zero.

In K1 line, the engine 10 is started in two steps in accordance with the first startup method for starting the engine 10 in series-parallel mode, whereas three steps are required in accordance with the second startup method for starting the engine 10 in series mode. Therefore, in the case of K1 line, the first startup method is employed.

In K2 line, three steps are required to start the engine 10 in accordance with the first startup method for starting the engine 10 in series-parallel mode; whereas two steps are required to start the engine 10 in accordance with the second startup method for starting the engine 10 in series mode. Therefore, the second startup method is employed in the case of K2 line.

In K3 line, two steps are required to start the engine 10 in accordance with the first startup method for starting the engine 10 in series-parallel mode; whereas four steps are required in accordance with the second startup method for starting the engine 10 in series mode. Therefore, the first startup method is employed in the case of K3 line.

The reason why the engine startup method is changed among K1 line to K3 line is that it is more desirable that an engine startup shock that is transmitted to the drive wheels is small in series mode because the transmission unit 40 is placed in the neutral state; however, it is required to consider that the clutch CS needs to be engaged in order to shift into the series mode. When the clutch CS is engaged at the time when the differential rotation between the rotating elements of the clutch CS is large, a shock at the time of the engagement increases, so an extra step of controlling the rotation speed of the first MG 20 such that Ng is equal to zero is required in such a case.

That is, because Ng is lower than zero in K1 line and K3 line, a step of setting Ng to zero is required in order to engage the clutch CS. In contrast, because Ng is almost equal to zero in K2 line, such a step is not necessary.

Hereinafter, a change in nomograph before and after an engine startup using the engine startup methods employed in K1 line to K3 line will be described.

FIG. 18 is a nomograph for illustrating an engine startup in one-motor EV mode (K1 line in FIG. 17). As shown in FIG. 18, in one-motor EV mode (K1 line in FIG. 17) before an engine startup, Ng is lower than zero as indicated by the common line L11 and the rotation speeds of S1 and CA1 are zero, so a shock is small even if the clutch C1 is engaged. Therefore, as a first step, the clutch C1 is initially engaged, and the state of the common line L11 is subsequently changed into the state of the common line L12 by causing the first MG 20 to generate the MG1 torque Tm1. Thus, the rotation speed of the engine 10 (that is, the rotation speed of CA1) is increased.

FIG. 19 is a nomograph for illustrating an engine startup in one-motor EV mode (K2 line in FIG. 17). As shown in FIG. 19, in one-motor EV mode (K2 line in FIG. 17) before an engine startup, Ng is almost equal to zero as indicated by the common line L21, so a shock is small even if the clutch CS is engaged. Therefore, as a first step, the clutch CS is initially engaged, the state of the common line L21 is subsequently changed into the state of the common line L22 by causing the first MG 20 to generate the MG1 torque Tm1. Thus, the rotation speed of the engine 10 (that is, the rotation speed of CA1) is increased.

FIG. 20 is a nomograph for illustrating an engine startup in two-motor EV mode (K3 line in FIG. 17). As shown in FIG. 20, in two-motor EV mode (K3 line in FIG. 17) before an engine startup, the clutch C1 and the brake B1 are engaged. At this time, because Ng is lower than zero as indicated by the common line L31, a shock is large if the clutch CS is engaged. On the other hand, because the rotation speeds of S1, CA1, and R1 are zero, a shock is small even if the brake B1 is released. Therefore, as a first step, the brake B1 is initially released, the state of the common line L31 is subsequently changed into the state of the common line L32 by causing the first MG 20 to generate the MG1 torque Tm1. Thus, the rotation speed of the engine 10 (that is, the rotation speed of CA1) is increased.

As described above, by selecting any one of the series mode and the series-parallel mode for starting the engine in response to the state before an engine startup, it is possible to reduce the number of steps of an engine startup, so it is possible to shorten the engine startup time.

The embodiment described above is illustrative and not restrictive in all respects. The scope of the invention is defined by the appended claims rather than the above description. The scope of the invention is intended to encompass all modifications within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A hybrid vehicle comprising: an internal combustion engine; a first rotary electric machine; a second rotary electric machine configured to output power to a drive wheel; a power transmission unit including an input element and an output element, the input element being configured to receive power from the internal combustion engine, the output element being configured to output power input to the input element, and the power transmission unit being configured to switch between a non-neutral state where power is transmitted between the input element and the output element and a neutral state where power is not transmitted between the input element and the output element; a differential unit including a first rotating element, a second rotating element and a third rotating element, the first rotating element being connected to the first rotary electric machine, the second rotating element being connected to the second rotary electric machine and the drive wheel, the third rotating element being connected to the output element, and the differential unit being configured such that, when rotation speeds of any two of the first rotating element, the second rotating element and the third rotating element are determined, a rotation speed of the remaining one of the first rotating element, the second rotating element and the third rotating element is determined; a clutch configured to switch between an engaged state where power is transmitted from the internal combustion engine to the first rotary electric machine and a released state where transmission of power from the internal combustion engine to the first rotary electric machine is interrupted, power from the internal combustion engine being transmitted to the first rotary electric machine through at least one of a first path or a second path, the first path being a path through which power is transmitted from the internal combustion engine to the first rotary electric machine via the power transmission unit and the differential unit, and the second path being a path through which power is transmitted from the internal combustion engine to the first rotary electric machine, the second path being different from the first path and not including the differential unit, and the clutch being provided in the second path; and a controller configured to control the internal combustion engine, the first rotary electric machine, the power transmission unit and the clutch, the controller being configured to: (i) set the power transmission unit to the neutral state, (ii) set the clutch to the engaged state, and (iii) then start the internal combustion engine by increasing a rotation speed of the internal combustion engine with the use of the first rotary electric machine.
 2. The hybrid vehicle according to claim 1, wherein the controller is configured to use any one of a first startup method for the internal combustion engine and a second startup method for the internal combustion engine in response to a state of the vehicle, the first startup method is executed while the power transmission unit is set to the non-neutral state, and the second startup method is executed while the power transmission unit is set to the neutral state, the clutch is set to the engaged state and then the rotation speed of the internal combustion engine is increased with the use of the first rotary electric machine.
 3. The hybrid vehicle according to claim 2, wherein the controller is configured to cause the vehicle to travel in a selected one of a plurality of operation modes, the plurality of operation modes include a series-parallel mode and a series mode, the series-parallel mode is a mode in which the power transmission unit is set to the non-neutral state and the clutch is set to the released state, the series mode is a mode in which the power transmission unit is set to the neutral state and the clutch is set to the engaged state, and the controller is configured to use the first startup method when the operation mode after a startup of the internal combustion engine is set to the series-parallel mode, and use the second startup method when the operation mode after a startup of the internal combustion engine is set to the series mode.
 4. The hybrid vehicle according to claim 2, wherein the controller is configured to change an operation characteristic of the vehicle based on one of the operation modes, which is selected through switch operation of a user, the operation modes include a first mode and a second mode, the first mode being an operation mode having a higher acceleration response of the vehicle than the second mode, and the controller is configured to use the first startup method when the user selects the first mode, and use the second startup method when the user selects the second mode.
 5. The hybrid vehicle according to claim 2, wherein the controller is configured to cause the vehicle to travel in a selected one of a plurality of operation modes, the plurality of operation modes include a first mode and a second mode, the first mode is a mode in which control is executed such that a rotation speed of the first rotary electric machine is zero, the second mode is a mode in which the rotation speed of the first rotary electric machine changes in response to a vehicle speed, and the controller is configured to use the second startup method when a rotation speed of the third rotating element is higher than a predetermined value, and use the first startup method when the rotation speed of the third rotating element is lower than or equal to the predetermined value.
 6. The hybrid vehicle according to claim 1, wherein the power transmission unit is configured to be able to change a ratio between a rotation speed of the input element and a rotation speed of the output element.
 7. The hybrid vehicle according to claim 1, wherein the power transmission unit is configured to be able to restrict rotation of the output element. 